641RM Series

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641RM Series

Dwyer Air Velocity Transmitter 641RM Series

Dwyer Air Velocity Transmitter


The Dwyer 641RM Series is the ideal instrument for monitoring air flow. This transmitter uses a heated mass flow sensor, which allows for precise velocity measurements at various flow rates and temperatures. The 641RM's 16 field-selectable ranges from 0-250 to 15,000 FPM (0-1.25 to 75 MPS) provide it the versatility to be selected for a multitude of applications. The unit's 6 ft. cable which connects the sensing probe with the electronic enclosure allows the enclosure to be mounted where it can be more easily accessed. Longer cable lengths are available for ducts that are at very high elevations from the plant floor. The optional LED produces a complete, compact solution for local indication of air flow.


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  • Clean room fresh air supply
  • HVAC air velocity measurements
  • Fan supply and exhaust tracking
  • Ensure proper lab hood exhaust flow rates

Power Requirements:12 to 35 VDC, 10 to 16 VAC, 1.5A rating required on supply due to initial power surge drawn by transmitter

Output Signal:4-20 mA, isolated 24V source, 3 or 4-wire connection

Output Filter: Selectable 0.5-15 sec.

Loop Resistance:600Ω max.

Current Consumption:300 mA max.

Cable Length:6.0 ft (1.8 m)

Accuracy:3% full scale process gas: 32° to 122℉ (0° to 50℃); 4% full scale process gas: -40° to 32℉ (-40° to 0℃) and 122° to 212℉ (50° to 100℃)

Response Time:1.5 sec. to 95% of final value (output filter set to minimum)

Display:4-1/2 digit 1/2″ red LED

Resolution:1 fpm, 0.01 mps (10 fpm @ 10,000 and 15,000 fpm ranges)

Electrical Connections:Screw Terminal

Mounting Orientation:Unit not position sensitive, probe must be aligned with airflow

Operating Temperature:Process: -40° to 212℉ (-40° to 100℃); Ambient: 32° to 140℉ (0° to 60℃)

Operating Humidity:non-condensing

Media Compatibility:Clean air and compatible, non-combustible gases

Operating Pressure:100 psi (690 kPa) max.

Power Requirements:12 to 35 VDC, 10 to 16 VAC; 1.5A rating required on supply due to initial power surge drawn by transmitter

Probe Length:12.0″ (30.5 cm)

Probe Diameter:5/16″ (0.79 cm)

Weight:0.9 lb (0.4 kg)